An organic electroluminescence device (hereinafter referred to as an “organic EL device”) utilizing an organic substance has a promising feature as an inexpensive, large-area full-color solid light-emitting display element, and many developments have been made on this type of organic EL device. Normally, an organic EL device is formed of an emitting layer and a pair of opposing electrodes holding the emitting layer therebetween.
When an electric field is applied between the both electrodes, electrons are injected from the cathode and holes are injected from the anode, these electrons are then recombined with the holes in the emitting layer, thereby to cause an excited state, and energy is discharged as light when the excited state is returned to the ground state.
Conventional organic EL devices have a higher driving voltage than an inorganic light-emitting diode. The luminance and luminous efficiency thereof are also low, and their properties tend to lower significantly. For these reasons, conventional organic EL devices have not been put in a practical use. However, as a result of studies made on organic materials constituting an organic EL device, the above-mentioned problems have been gradually improved in recently-developed organic EL devices.
As an organic material constituting an organic EL device, a compound having a pyrromethene skeleton has been studied, for example (Patent Documents 1 to 5, for example). However, further improvement in luminous efficiency or the like has been demanded.